Monday, November 21, 2011

THREE WEEKS LATER

We have now completed work at 13 stations (Fig.1) and completed 14 CTD casts, 15 MOCNESS tows, and 14 IKMT tows. We are on track – in terms of progress through our cruise plan – to complete work at nearly all of our planned stations. At this writing, we are heading back into the open waters of Drake Passage with the goal of working at four deep-water locations (Stns #6, #5, #4, and #24), two shelf stations (#23 and #3), and a station in protected waters of Gerlache Strait.

Figure 1. Station locations for LMG11-10. As of 20 Nov 2011, work has
been completed at stations shown with circled station numbers. The
cruise track and order of stations were changed to accommodate weather.
The star shows the ship’s location at 8:00 pm on Nov. 20th.

Our cruise has already been very successful. Our samples from vertically-stratified MOCNESS tows at each station are yielding a useful view of the pelagic community of the Drake Passage and Bransfield Strait. Taxonomic analysis of these quantitative samples will help us characterize the early spring assemblage of the Western Antarctic Peninsula region. We will compare our findings with an earlier study, the comprehensive US GLOBEC Southern Ocean Program carried out during Fall and Winter, 2001 and 2002. Peter Wiebe led four US GLOBEC cruises as chief scientist; he collected zooplankton samples using a MOCNESS just like the one we are using now and equipped with strobe lights to reduce net avoidance by krill.

Our nets have brought up huge catches of krill, usually in surface nets sampling during the dark, have contrasted with generally sparse MOCNESS and IKMT samples. We have caught only a small number of salps. Our team has processed 65 aggregates and 10 solitaries – some of them exceptionally large and packed with embryos, which can quickly generate a population “bloom” of chain-forming aggregates. Other specimens collected, identified, and flash-frozen for genomic and transcriptomic analysis (please look up the definitions of those terms yourself) include ~300 individuals of Euphausia superba (including larval, juvenile, and adult stages), with the telson (tail) preserved separately in alcohol, so individuals can used for analysis of cohort (life stage) structure. We have also flash-frozen various zooplankton that caught our interest, including copepods, gastropods, ctenophores, and amphipods, among others.

Our goal is to obtain material for genomic and transcriptomic analysis, especially for the Southern Ocean salp. The best source of material for these analyses is from our IKMT tows, which are shallower and usually yield living zooplankton. These specimens are identified and flash-frozen for analysis at UConn.

Why so few salps this year? In December 2004, salp researchers caught tens of thousands of salps, which they caught live by SCUBA diving! In December 2010, hundreds of salps were caught at many of the same locations we are visiting this year. We speculate that the Spring population increase of salps may be delayed this year. Several knowledgable people have remarked on the late ice cover this year of coastal waters of the Western Antarctic Peninsula region.

So our salp hunt continues, and we are looking forward to seeing what the open shelf and offshore waters may hold.